20x25x1 (Approx 18 1/2 x 22 1/2) Aftermarket Dynamic Replacement Filter (3 Pack) 97% efficient for particles down to 0.3 microns in size. Removes allergens such as pollen, mold spores, dust mite pellets and other contaminants that other filters miss, including bacteria, smoke and other odors. Contains electronic polarized media to provide maximum ozone-free air cleaning. When particles and volatile organic compounds (VOC's) pass through the filter system, they become polarized. These polarized particles join together to form bigger clusters that are more easily captured and collect on a disposable fiberglass medium pad with an activated carbon center screen. Do not measure the pad itself! Panel size is labeled on the black track of your panel. Please order your pads using this panel size. Change filter every 3 to 4 months. These are quality aftermarket filters.